Lesson 1: PLANT CELLS AND TISSUES

Robert Whittaker

s  During the late twentieth century, Robert Whittaker's five-kingdom system was a standard feature of biology textbooks, serving as an important organizing scheme for discussing biodiversity.

5 Kingdom of Classifications

Ø  Monera

Ø  Protista

Ø  Fungi

Ø  Animalia

Ø  Plantae (Botany)

CELLS

Cell, in biology, is the basic membrane-bound unit that contains the fundamental molecules of life and of which all living things are composed.

A single cell is often a complete organism in itself, such as a bacterium or yeast.

Other cells acquire specialized functions as they mature.

PROKARYOTIC CELL

PRO- before

KARYON – nucleus

EUKARYOTIC CELL

EU – well or good

ANIMAL CELL VS. PLANT CELL

WHAT IS A PLANT CELLS?

Plant cells are eukaryotic cells that vary in several fundamental factors from other eukaryotic organisms.

Both plant and animal cells contain a nucleus along with similar organelles.

One of the distinctive aspects of a plant cell is the presence of a cell wall outside the cell membrane.

PLANT CELL STRUCTURE

CELL WALL

s  a rigid layer that is composed of polysaccharides cellulose, pectin, proteins and hemicellulose.

s  it is located outside the cell membrane

s  to protect and provide structural support to the cell.

PLASMA MEMBRANE

s  involved in the production and assembly of cellulose for cell walls.

NUCLEUS

s  a membrane-bound structure that is present only in eukaryotic cells.

s  vital function of a nucleus is to store DNA or hereditary information required for cell division, metabolism, and growth.

1.        Nucleolus: it manufactures cells' protein-producing structures and ribosomes.

2.        Nucleopore: allow proteins and nucleic acids to pass through.

s  Nuclear Envelope

s  Nucleoplasm

ENDOPLASMIC RETICULUM

s  the outer membrane of the nucleus is connected to and continuous with the endoplasmic reticulum

s  the endoplasmic reticulum facilitates cellular communication and channeling of materials

s  many important activities, such as the synthesis of membranes for other organelles and modification of proteins from components assembled from elsewhere within the cell, occur either on the surface of the endoplasmic reticulum or within its compartments.

RIBOSOMES

s  typically roughly ellipsoidal in shape with apparently varied and complex surfaces

s  each ribosome is composed of two sub-units that are composed of RNA and proteins

s  functions as a micro-machine for making proteins.

s  they are the smallest membrane-bound organelles that comprise RNA and protein.

s  they are the sites for protein synthesis, hence, also referred to as the protein factories of the cell.

DICTYOSOMES – Golgi Bodies

s  post office of the cell

s  stacks of flattened discs or vesicles known as dictyosomes may be scattered throughout the cytoplasm of a cell.

s  involved in the modification of carbohydrates attached to proteins that are synthesized and packaged in the endoplasmic reticulum.

PLASTIDS

s  they are membrane-bound organelles that have their own DNA.

s  necessary to store starch and to carry out the process of photosynthesis

1.        CHROMOPLASTS: are heterogeneous, colored plastid which is responsible for pigment synthesis and for storage in photosynthetic eukaryotic organisms

Chromoplasts have red, orange, and yellow colored pigments which provide color to all ripe fruits and flowers.

2.        CHLOROPLASTS: elongated organelle enclosed by phospholipid membrane

The chloroplast is shaped like a disc and the stroma is the fluid within the chloroplast that comprises circular DNA

The chlorophyll absorbs light energy from the sun and uses it to transform carbon dioxide and water into glucose.

Corkscrew-like ribbons shaped; cells of the green algae Spirogyra.

Bracelet-shaped chloroplasts: other green algae, such as Ulothrix.

Within the chloroplast are numerous GRANA (singular: granum), which are formed from membranes and have the appearance of stacks of coins with double membranes

There are usually about 40 to 60 grana linked together by arms in each chloroplast, and each granum may contain from two or three to more than 100 stacked THYLAKOIDS

The liquid portion of the chloroplast is a colorless fluid matrix called STROMA

3.        LEUCOPLAST: they are found in the non-photosynthetic tissue of plants.

Amyloplasts

Elaioplasts

If exposed to light, some leucoplasts will develop into chloroplasts, and vice versa.

They are used for the storage of protein, lipids, and starch.

CENTRAL VACUOLE

s  Tonoplast is a membrane that surrounds the central vacuole.

s  The vital function of the central vacuole, for storage and to sustain turgor pressure against the cell wall.

s  The central vacuole consists of cell sap.

Crystals occurs in various shapes and size. They are differentiated based on their composition and shape.

Calcium oxalate crystals in the stem and leaf of Cynanchum acutum (Stranglewort)

(A-C) Druse crystals in the cortex of the stem at different magnifications. (D) Druse crystals in the leaf mesophyll. (E) Druse crystals around the major vein. (F) Druse and prismatic crystals along the vascular bundle.

Calcium oxalate (CaC₂0₄):

RAPHIDE: fine, needle-like crystals occurring singly or in clusters, scattered or enclosed in a sac as in gabi or other succulent plants

PRISMATIC: prism-like or diamond-like crystals found in leaves of begonia or Bangka-bangkaan

ROSETTE: flowerlike appearance in santan and stem of kutsarita plant

STYLOID: knife-like, tapering at both ends

Calcium carbonate (CaCO₃):

CYSTOLITH: grapelike as seen in the hypodermal cell of the leaf of an Indian rubber tree or ampalaya-like plant.

Specialized Plant Cell Types

Collenchyma Cells

Ø  they are hard or rigid cells, which play a primary role in providing support to the plants when there is restraining growth in a plant due to a lack of hardening agent in primary walls.

Sclerenchyma Cells

Ø  more rigid compared to collenchyma cells and this is because of the presence of a hardening agent. These cells are usually found in all plant roots and are mainly involved in providing support to plants

Xylem Cells

Ø  the transport cells in vascular plants.

Ø  they help in the transport of water and minerals from the roots to the leaves and other parts of the plants.

Phloem Cells

Ø  Phloem cells are other transport cells in vascular plants. They transport food prepared by the leaves to different parts of the plants.

Plant Cell Functions

PHOTOSYNTHESIS

s  the process in which light energy is converted to chemical energy in the form of sugars.

s  The Light-dependent reaction which stores energy from the sun through the form of ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate).

s  The Calvin cycle reactions can be organized into three basic stages fixation, reduction, and regeneration.

Lesson 2: PLANT TISSUE

Permanent: THREE BASIC TYPES OF PLANT TISSUES

a.        Parenchyma Tissue

b.        Collenchyma Tissue

c.        Sclerenchyma Tissue

Types of Parenchyma Tissue

s  Normal Parenchyma Cells

s  Rounded

s  Angular

s  Prosenchyma

s  Xylem Parenchyma

s  Epidermal Cells

s  Mesophyll

s  Aerenchyma

Types of Sclereids:

s  Stone cell branchysclereid, with pit canals

s  Macrosclereid

s  Osteosclereid

s  Astrosclereid

s  Fillform sclereid

Plant Tissues

Types:

Ø  Meristematic tissue

Ø  Permanent (or non-meristematic) tissue.

Meristematic VS Permanent Tissue

Meristematic tissue is analogous to stem cells in animals. meristematic cells are undifferentiated and continue to divide and contribute to the growth of the plant (cell division). In contrast, permanent tissue consists of plant cells that are no longer actively dividing.

PLANT TISSUES

Meristems produce cells that quickly differentiate, or specialize, and become permanent tissue.

Such cells take on specific roles and lose their ability to divide further.

They differentiate into three main tissue types: dermal, vascular, and ground tissue.

Each plant organ (roots, stems, leaves) contains all three tissue types.

Simple Permanent Tissue

1.        Epidermis is the outermost layer of any plant organ with primary growth.

Ø  Specialized cells present in the epidermis are the guard cells of the stomata. The outward growth of epidermal cells is known as epidermal hair or trichome.

Ø  The epidermis produces a waxy material called cuticle.

Ø  Epidermis on stems and leaves prevent water loss by transpiration.

2.        Parenchyma is the least specialized permanent tissue composed of living thin-walled cells.

Ø  These cells help to synthesize and store organic products in the plant.

Ø  The middle tissue laver of leaves (mesophyll) is composed of parenchyma cells, and it is this layer that contains plant chloroplasts,

Ø  Chlorenchyma are elongated cylindrical cells with long axis at the right angle to the surface of the organ.

Ø  Aerenchyma are specialized for gas exchange.

3.        Collenchyma cells have a support function in plants, particularly in young plants.

Ø  These cells help to support plants, while not restraining growth.

Ø  Collenchyma cells are elongated in shape and have thick primary cell walls composed of the carbohydrate polymers cellulose and pectin.

Ø  able to stretch along with a plant as it grows.

Ø  Collenchyma cells are found in the cortex (layer between the epidermis and vascular tissue) of stems and along leaf veins.

4.        Sclerenchyma cells also have a support function in plants, but unlike collenchyma cells, they have a hardening agent in their cell walls and are much more rigid.

Ø  Sclereids have varied sizes and shapes, and most of the volume of these cells is taken up by the cell wall.

Ø  Fibers are elongated, slender cells that are strand-like in appearance. Fibers are strong and flexible and are found in stems, roots, fruit walls, and leaf vascular bundles.

5.        Cork is the outer impermeable protective layer of a secondary plant body.

Ø  It is composed of compactly arranged dead lignified and suberized cells without intercellular spaces.

Complex Permanent Tissue

1.        Water-conducting cells of the xylem have a support function in plants.

Xylem has a hardening agent in the tissue that makes it rigid and capable of functioning in structural support and transportation.

The main function of the xylem is to transport water throughout the plant.

Two types of narrow, elongated cells compos xylem: tracheids and vessel elements

Tracheids have hardened secondary cell wall. and function in water conduction.

Vessel Elements resemble open-ended tubes that are arranged end to end allowing water flow within the tubes.

2.        Vascular plants also have another type of conducting tissue called phloem. Sieve tube elements are the conducting cells of phloem.

They transport organic nutrients, such as glucose, throughout the plant. The cells of sieve tube elements have few organelles allowing for easier passage of nutrients.

Since sieve tube elements lack organelles, such as ribosomes and vacuoles, specialized parenchyma cells, called companion cells, must carry out metabolic functions for sieve tube elements.